subterrestrial

Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

adj. Subterranean; underground.

from Wiktionary, Creative Commons Attribution/Share-Alike License

adj. Under the earth; subterranean.

from the GNU version of the Collaborative International Dictionary of English

adj. Subterranean.

from The Century Dictionary and Cyclopedia

Subterranean.

Etymologies

sub- +‎ terrestrial (Wiktionary)

Examples

Richard Shaver, for instance, stated that subterrestrial beings he "knew" about were in possession of advanced technology that created seemingly solid (holographic) images, such as space ships (UFOs), along with other more sinister mind-altering machines.

Horace), is proper only to be frequented by princes and other great men in the highest affluence of fortune; the subterrestrial is appointed for the entertainment of the poorer sort of people only, whom Horace advises,